Had a similar error on a Win XP x86 SP3 dual core system on 4thJan11.
Both wingmen returned the result without any problems and it was a one off event; other tasks have returned on that system since, no other errors. I'm not looking for a solution, as I think its just a one-off error (system restart, lockup, installation, who knows), just posting on the off chance that others have a similar problem. Will edit if I find cause from logs.

HFCC_ L4_ 00115769_ L4_ 0000_ 0--

Can't acquire lockfile - exiting
FILE_LOCK::unlock(): close failed.: No error


Result Log

Result Name: HFCC_ L4_ 00115769_ L4_ 0000_ 0--
<core_client_version>6.10.18</core_client_version>
<![CDATA[
<message>
too many exit(0)s
</message>
<stderr_txt>
Failed to get VersionInfo size: 1812
INFO:[03:33:17] Start AutoGrid...
Can't acquire lockfile - exiting
FILE_LOCK::unlock(): close failed.: No error
Can't acquire lockfile - exiting
FILE_LOCK::unlock(): close failed.: No error
Can't acquire lockfile - exiting
FILE_LOCK::unlock(): close failed.: No error
Can't acquire lockfile - exiting
FILE_LOCK::unlock(): close failed.: No error
Can't acquire lockfile - exiting
...
Can't acquire lockfile - exiting
FILE_LOCK::unlock(): close failed.: No error

</stderr_txt>
]]>